1. Field of the Invention
The present invention relates to a semiconductor packaging structure and fabrication method thereof, and more specifically to a thermally enhanced packaging structure and fabrication method thereof.
2. Description of the Related Art
A conventional semiconductor package is attached to a printed circuit board (PCB) of an electronic product by using surface mount technology (SMT). SMT usually comprises applying a solder paste on a pad of the PCB, putting the package onto the solder paste for connecting the contact of the package and the wiring of the PCB, and then proceeding the reflow process. The reflow process is heating the PCB up to the melting point of the solder paste, and cooling the melting solder paste to achieve soldering the package's contact and the pad. The package has normally experienced the reflow process at least once when the electronic product is finished.
When using eutectic tin-lead alloy as solder paste, the melting point is approximately 183° C., and peak temperature during the reflow process is usually between 220° C. and 240° C. However, using lead-free solder paste is necessary to obey the requirements of Green product. The common materials are tin-silver alloy and tin-silver-copper alloy. When using the common lead-free solder paste, the melting point is between 215° C. and 220° C., and peak temperature during the reflow process is usually approximately 250° C. The peak temperature is sufficient to thermally deform the package and PCB, and retains stress between the package and PCB after the reflow process, which would negatively affect the reliability of the package and the electronic product.
Take digital camera as an example. Image captured products such as digital cameras include image ICs, and each image IC has an image sensor. The image sensor is a heat sensitive device and is often damaged during the reflow process, which affects the reliability of the package of the image IC and image-captured product.
Due to the demand for small and light electronic products, it is necessary to lay out more devices on limited semiconductor substrates of IC chips. That would be a challenge for heat dissipation of the package. To dissipate heat from a non-image IC package, a heat-conductive sheet or heat sink may be disposed on the encapsulant of the package, or some thermal contacts of a package can be provided to conduct the heat to the PCB. However, setting the heat-conductive sheet/heat sink on the encapsulant complicates encapsulant formation, and the ambient moisture may diffuse in the package along the interface between the heat-conductive sheet/heat sink and encapsulant to affect reliability of the package. Moreover, because the cross-sectional area of the thermal contact is small, when the thermal contact is provided in the package, the effect of heat dissipation is limited.
In a conventional image IC package, the image IC is covered by a transparent material, making it difficult to set a heat-conductive sheet or heat sink thereon. Therefore, the provision of heat contacts is the only way for heat dissipation of the image IC package. The effect thereof is limited.